Alistair Darling, the Chancellor, said he smoked it: "Occasionally in my youth".

Andy Burnham, Treasury Chief Secretary, admitted he had smoked it "once or twice at university", while Ruth Kelly, Transport Secretary, a devout Catholic, smoked the drug in her youth, but realised it was "foolish and gave up".

A spokesman for John Hutton, the Business and Enterprise Secretary, said he smoked cannabis when he was at university over 30 years ago. "He regrets doing it now."

Hazel Blears, the Communities secretary, and Yvette Cooper, the Housing Minister, who attends cabinet, are on record as admitting having tried drugs.

Alan Johnson, the Health Secretary, remarked that he "did the sex and rock and roll but not the drugs’’ during his youth.

Tony McNulty, Miss Smith's Home Office minister, also admitted smoking the drug at university when asked today.

"I think anyone who went to university in the late 70s, early 80s would have encountered and may have consumed cannabis. I certainly did," he said.

The Advisory Committee on the Misuse of Drugs is to consider whether powerful new strains of cannabis mean that it should be moved back to Class B. It was placed in Class C three years ago after a review requested by David Blunkett when he was Home Secretary.

Shortly before the last election in 2005, Mr Clarke asked for the issue to be reconsidered. In January last year, the committee recommended keeping it in Class C, which carries lesser penalties for possession and dealing.

It conceded that regular cannabis use can have "real and significant" mental health effects. The modern form of the drug is far more potent than that used in the 1960s because of the high content of THC, the ingredient that provides the "buzz".

But advisers, who include leading medical specialists, concluded that it was unlikely to cause schizophrenia. The committee said that while cannabis could produce harmful effects, these were "not of the same order as those of substances within Class B".

The Home Secretary is preparing a consultation on drugs laws. The Government's 10-year drugs strategy runs out next year and is being reviewed. Miss Smith will ask the public to comment on ways to improve drugs education, treatment and bear down on dealers.

The Government move was seen as another retreat from the Blair legacy and a response to the drugs warning from a Tory policy team last week.

The Home Office said the review would consider reports that the danger from cannabis is increasing because of stronger strains like "skunk".

Supporters of a more liberal regime accused Mr Brown of political posturing. A spokesman for the Transform pressure group said: "The potency issue and the mental health issues associated with cannabis are well understood and have not changed significantly since they were last reviewed in 2005."

David Davis, the shadow home secretary, said: "We have long called for the reclassification of cannabis based on the science and evidence available which shows all too clearly the real damage this drug can do to people – especially young people."

Keith Hellawell, the former Government "drugs tsar" who resigned over the original reclassification, said: "There was never any justification for reclassifying."

Marjorie Wallace, of Sane, the mental health charity, said: "Urgent action is needed to prevent an epidemic of drug-induced psychosis, and Sane welcomes this consultation on drugs strategy and the classification of cannabis."

Mr Blunkett said he was "quite relaxed" about the latest review, saying it was understandable that a new prime minister and home secretary would want to take a look at all important areas of public policy.

It is estimated that as many as 500,000 individuals in Britain may use the drug regularly. Some have developed schizophrenia-like symptoms and mental health hospital admissions due to cannabis have risen by 63 per cent in the past five years.